1) Field of the Disclosure
The disclosure relates generally to modal analysis assemblies, systems and methods, and more particularly, to a modal impact testing assembly, system and method for testing a rotating element at operational speeds.
2) Description of Related Art
Modal analysis is often used to test and analyze equipment and machinery used in the manufacture of structures and component parts in the aerospace, automotive, and structural engineering and design industries, as well as other industries. Modal analysis includes modal testing of a mechanical structure, which involves acquiring, measuring and analyzing dynamic characteristics of the mechanical structure when excited by an input. For example, modal testing may be used to determine the natural mode shapes and frequencies of a mechanical structure during free vibration in order to assess the potential for structural dynamic issues, such as fatigue, vibration and noise.
A known system and method of modal testing includes modal impact testing, such as impact hammer testing. Impact hammer testing uses a hammer device with a load cell to measure the force of an impact on a test structure. Impact hammer testing has been used to perform modal impact testing of rotating elements, such as spindles, of rotating cutting machines used for machining metallic fittings or other component parts, or of other machining tool devices. Such impact hammer testing may be used to determine precise operational behavior and operating parameters of the rotating cutting machines or other machining tool devices. The impact hammer testing of the rotating elements, such as the spindles, typically involves an operator manually impacting a stationary spindle with a hand-held, impact hammer and using an accelerometer to provide a response signal.
However, in order to operate successfully at elevated speeds, certain spindles may change their bearing preload values depending on their speed of rotation. As used herein, “bearing preload value” means the amount of load placed on rolling elements or ball bearings in the spindle that enable the spindle to rotate, before the application of any external loads. Such change in bearing preload values may alter the outcome of the modal impact testing. This may, in turn, hinder the determination of accurate operational behavior and operating parameters of the rotating cutting machines or other machining tool devices undergoing modal impact testing. Previously, even with the old impact hammer testing, weeks and months of test manufacturing and production runs are needed to properly characterize static and dynamic manufacturing performance of operationally rotating spindles.
Thus, for such spindles, in order to obtain accurate operational behavior and operating parameters of the rotating cutting machines or other machining tool devices undergoing modal impact testing, a system or method of modal impact testing is needed that is performed while the spindle is rotating at operational speeds. However, manually impacting a rotating spindle requires that the operator be in close proximity to the rotating spindle and the rotating cutting machine during the modal impact testing. This may result in increased risk to the operator. Moreover, if an accelerometer is used in the modal impact testing, such accelerometer typically requires the use of connector elements, such as wires, to be connected between the accelerometer and the spindle. However, it may be difficult, if not impossible, to attach connector elements, such as wires, to a rotating spindle.
Accordingly, there is a need in the art for an improved modal impact testing assembly, system and method for modal impact testing of a rotating test element at operational speeds that provides advantages over known assemblies, systems and methods.